1. Field of the Invention
The present invention relates to a control device for scattering agricultural chemicals by fumigation especially in a hothouse such as a vinyl plastic hothouse for cultivating crops. In particular, the present invention relates to a fumigation type control device for scattering agricultural chemicals which can keep the temperature of the agricultural chemicals uniform when fumigating and scattering the agricultural chemicals by heating them, and whereby a plurality of control devices can be simultaneously operated to prevent the excessive flow of starting current at an initial power-on stage.
2. Description of the Prior Art
The control device for scattering the agricultural chemicals for destroying germs may be classified into a spray type and a fumigation type. The spray type control device is used for scattering the agricultural chemicals diluted with a large quantity of water utilizing a sprayer. However, the spray type control device is generally used in scattering the agricultural chemicals onto the crops cultivated on the exposed land, but is improper for use in scattering the agricultural chemicals onto the crops cultivated within an airtight space such as a hothouse.
The fumigation type control device is used for evaporating the agricultural chemicals by heating them and scattering the evaporated chemicals onto the crops. The fumigation type control device has a superior insecticidal effect since the evaporated chemicals act on the germs as minute particles, and can be implemented by a simple device. Also, since the fumigation type control device enables the scattering to be performed at night when farmers do not work, it has been mainly used for scattering in an airtight space such as a vinyl plastic hothouse, a greenhouse, and the like.
The fumigation type control device may also be classified into one using an electric lamp as its heating element, and the other using a nichrome wire as its heating element. The electric lamp, which radiates light and heat when it is turned on, heats and fumigates the agricultural chemicals. However, the electric lamp suffers from a large power consumption due to the radiation of light. Particularly, the electric lamp consumes more than 100 W in power, whereas the other fumigation type control device typically requires only about 35 W. Further, the electric lamp has no function for adjusting the temperature of the agricultural chemicals, and thus the temperature range of the heated chemicals greatly varies according to the room temperature of the hothouse and the variation of the voltage supplied to the electric lamp. As a result, the fumigation type control device using the electric lamp as its heating element may be used without a problem in regions where the quality of the electric power is good and the temperature variation in the hothouse is small, but it cannot be suitably used otherwise.
A fumigation type control device for heating and evaporating the agricultural chemical using a nichrome wire as its heating element is disclosed in Korean Utility Model Laid-open No. 95-29140. FIG. 1 illustrates the fumigation type control device disclosed in Korean Utility Model Laid-open No. 95-29140.
Referring to FIG. 1, a plurality of coupling rods 3, which are fixed along the outer periphery of a main body 1 of the control device, are coupled to a coupling bracket 5. On the center of the coupling bracket 5 is provided a link 7. In FIGS. 1-2, the reference numeral 9 denotes a storage tank for storing agricultural chemicals to be fumigated, and reference numeral 11 denotes a protective barrel installed inside the main body I to protect the storage tank 9.
On the bottom surface of the protective barrel 11, a heating element 13 is provided which is a nichrome wire for heating the agricultural chemicals in the storage tank 9 by generating heat when the power is supplied thereto. Also, on the outer surface of the main body 1 are provided a temperature adjustor 15 for manually controlling the heating temperature of the heating element 13 and a power switch for switching the power supply to the heating element 13.
The operation of the conventional fumigation type control device as constructed above will be explained. The link 7 of the control device is suspended in a predetermined position so that the control device is maintained in horizontal orientation. If the power switch 17 is turned on, power is supplied to the heating element 13, causing the heating element 13 to generate heat. Accordingly, the agricultural chemicals stored in the storage tank 9 are heated and evaporated, and then the evaporated agricultural chemicals are scattered onto the cultivated crops to destroy germs.
At this time, a user manipulates the temperature adjustor 15 for controlling the power supply to the heating element 13, so that the agricultural chemicals are heated and evaporated at a proper temperature.
According to the conventional control device as described above, it is difficult to heat the agricultural chemicals to a proper desired temperature due to the voltage variation of the supplied power, the variation of the environmental temperature, and the variation of the temperature adjustor 15 itself. Further, the contacts of the temperature adjustor 15 are apt to corrode by highly corrosive gases produced during fumigation of the agricultural chemicals in the hothouse, the high temperature and high humidity environment, and various harmful gases existing in the hothouse. Such corrosion may cause the temperature adjustor 15 to malfunction.
Typically, most agricultural chemicals are kept in a liquid state. However, a powdered agricultural chemical such as sulfur may be liquidized by heating, or solidified and expanded if it gets cold. Accordingly, if the powdered agricultural chemical gets cold, it may expand the flat bottom surface of the storage tank 9, causing the bottom surface of the storage tank 9 to droop downwards, and reduce the heat transfer area of the heating element 13.
Further, since the inside diameter of the upper portion of the storage tank 9 and the lower portion thereof are designed to be the same, it is difficult to fit the storage tank 9 into the protective barrel 11, causing the heat produced from the heating element 13 to easily exhaust through the gap formed between the storage tank 9 and the protective barrel 11.